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Re: Twisting of rebar

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David,
 
Heating the rebars degrees may lower the strength of concrete (at 600 degrees - about 40%; at 1000 degrees - up to 80%). Besides, it is very hard to control the temperature (especially this time of the year) in the field.
 
It appears that permanent twisting of a 12" long #5 rebar can be achieved elastically - say (for the sake of argument) even to the shear stress of Fy - to a total angle of about 6 degrees.  After that, the deformations are plastic, so even if the rebar will survive the 90-degree twisting, it cannot be really relied upon.  Additionally, any considerable twisting will affect the concrete around the rebar, especially, close to the "fixity" surface.
 
Neither of your options appears quite acceptable; you may want to consider cutting the rebars altogether and epoxying a whole new set of reinforcement.  Even in a high wind area a concrete roof should not develop too much of net uplift.
 
A final crazy thought - why can't you leave the rebars as they are?
 
 V. Steve Gordin, SE
Irvine CA     
 
 
 
 
----- Original Message -----
Sent: Thursday, November 06, 2008 07:25
Subject: Twisting of rebar

Is there an ACI document that specifies the amount that a bar can be
twisted?

Hooked bars extend out of the top of a load-bearing 12" concrete wall.
The concrete roof slab has not been placed yet.  The hooks are intended
to be perpendicular to the wall, but have been placed parallel.  I
recommended that the bars be heated to 1350-1400F, straightened, and
then bent in the correct direction.  The contractor would prefer to
grasp the bar at the point where it protrudes from the concrete and
twist the bar 90 degrees.  The bar extends approx. 12" above the level
of the concrete, so 90 degrees of twisting in a #5 bar would be
occurring over a 12" length. 

I am entertaining this proposal because another case of heating and
bending bars on this job (without my approval) turned out to be a
disaster.

Thanks,

David Dickey, P.E.
Lexington, KY

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